a {
    text-decoration: none;
}
a:link{
     color: black;
     background-color: yellow;
}
a:hover {
    /*鼠标悬停*/
    color: red;
}
a:visited {
    /*访问后的链接*/
    color: #999999;
}
a:active {
    /*激活状态*/
    color:darkgreen;
}
